The recent publication in the US of a state of the industry report entitled ‘North American Mass Timber’* merits attention. At 156-pages, this is a serious piece of work, hugely detailed and predictive of further exponential growth in the use of mass timber products and systems between now and 2034.
As a continent that took some time to come around to the modern construction potential of these technologies, the recent rapidity of industry development there is truly astonishing and hugely impressive. But more later on what has brought this about.
North America is not alone in witnessing advances – and political interventions – to promote greater use of timber (and mass timber in particular). Huge investment in large new cross-laminated timber (CLT) manufacturing facilities is evident in many corners of the globe – everywhere that is, except the UK (and more on that later too).
From Austria to Australia, France to Brazil, Sweden to South Africa, the vision for future construction is the same; an anticipation of many more buildings – and building types – employing one or more solid laminate timber systems in their construction. New hybrid timber construction concepts involving concrete and/or steel continue to emerge too, but wood is undoubtedly the key selling point.
Climate change, carbon sequestration and greater use of the world’s principal renewable building material underlie much of this transformation in material and product preferences, but increasing emphasis on modern methods of construction (MMC), offsite manufacture (OSM) and design for manufacture and assembly (DfMA) have also radically altered perceptions of how the built environment should – and can – be formed from wood in the second quarter of the 21st century.
So, what are the key factors that are so dramatically changing large parts of the international construction landscape?
The benefits of mass timber construction are well documented, for example, offsite fabrication of large format solid timber panels with openings and service channels pre-cut using parametric modelling and CNC machines, precision manufacture ensuring good airtightness and strong thermal performance, speed of erection, almost zero waste, very low onsite noise, plus reduced number of deliveries to site, reduced foundations due to the lighter weight of solid wood structures, reduced numbers of site operatives and, perhaps the most important of all, the capacity to build tall.
The previous seven-storey limitations of platform timber frame have long been exceeded. In the 12 years since the ninestorey, CLT Stadthaus in Hackney by Waugh Thistleton Architects rocked the construction world, design focus has been on the potential to build ever-higher timber structures. Currently, the tallest modern timber structure in the world is the Mjøstårnet Tower in Norway which, at 18-storeys/85.4m, has established a new international threshold for tall timber buildings.
In the US, the International Code Council’s 2021 Building Code will allow the use of mass timber in buildings up to 18 storeys high. In a country where many states previously restricted timber construction to six storeys, these changes may appear radical but they have not emerged in isolation. In part they are driven by designer and developer demand, but they can also be traced back to president Obama’s sponsorship of an architectural competition to promote greater use of timber in tall buildings.
Alongside this, and sensing the opportunity this new technology offered to the US timber industry, the Senate promoted a Tall Timber Act. This subsequently emerged as the Timber Innovation Act, signed off by president Trump in December 2018. Almost immediately afterwards California announced a design competition for tall timber buildings and recently passed legislation to endorse the ICC 2021 height limits within the state’s own building codes. In doing so, it joined a growing list of US states, including Georgia, Oregon and Washington, that have already taken this path.
The North American Mass Timber report suggests the number of mass timber buildings in the US alone is expected to double every two years through to 2034 and the ICC Code changes are one of the justifications given for recommending manufacturers to invest in production capacity, a challenge more than met by the industry-disruptive ambitions of Katerra. Its US$150m, 270,00ft2, state-of-the-art CLT plant on a 29-acre site in Spokane, Washington, currently houses the world’s largest CLT press.
It is not alone. New CLT plants are being established at pace throughout North America, including Element5’s fully automated 125,000ft2 plant at St Thomas, Ontario, which opens later this year.
Elsewhere, political action has been a motivating force for change. In France, Adivbois, the public-private alliance to promote timber-based construction is supporting building of exemplar developments across the country. The French government also recently announced that all new public buildings must be constructed from 50%+ of timber products/systems and, in a separate move, it was announced that sports and other facilities due to be constructed for the 2024 Paris Olympic Games must be built of timber.
So why is the UK so dilatory in participating in this international impetus towards advanced timber manufacturing and construction technology?
First, the country has never properly engaged in large-scale commercial production of any solid laminate timber system. Investment on a comparative scale to European manufacturers has never materialised, other than for L&G’s subsequently aborted plan to make CLT on an industrial scale in a large facility near Leeds. Consequently, and despite having sufficient suitable production forestry to sustain a commercially viable plant for 30+ years, almost all of the mass timber products and systems used in this country are imported.
The fallout from the Grenfell Tower fire has also adversely affected the UK timber construction sector. Prior to this tragic event, London had arguably become the international epicentre for innovation in mass timber design and construction. But despite having no structural timber or cladding, subsequent regulatory changes for England and Wales introduced post-Grenfell by the UK government not only effectively banned combustible material in the wall structure of projects over 18m tall (with the proposal that this is reduced to 11m), they have also disproportionately impacted on the mass timber sector.
Whilst intense lobbying to redress this regressive legislation continues, there is no doubt the hiatus has prompted considerable negativity towards the use of mass timber amongst UK developers, lenders, insurers, planners and building regulations officials.
The third critical issue is the vacuum in professional education on this subject. Despite CLT being in use in the UK for over 20 years, it and other mass timber technologies are still substantially absent from the curricula of university architecture school and engineering departments. The lack of investment in independent objective information, training and R&D in this crucially important subject is not only an industry issue, but a national economic one too. In 2016, Mark Farmer’s report ‘Modernise or Die’,** highlighted the looming catastrophe for the construction industry if it failed to invest in education and skills training but, four years on, this remains largely the case.
To address this deficiency, Timber Design Initiatives Ltd established the Mass Timber Academy (https://www.masstimberacademy. com) at the beginning of 2020. Interrupted by the Covid-19 lockdown, its inaugural programme covering all aspects of mass timber design and construction will restart in early 2021, prefaced by an autumn series of introductory online activities.
